Abstract
Sharply thermo- and pH-responsive pentablock terpolymer with a core-shell-corona structure was prepared by RAFT polymerization of N-isopropylacrylamide and methacrylic acid monomers using PEG-based benzoate-type of RAFT agent. The PEG-based RAFT agent could be easily synthesized by dihydroxyl-capped PEG with 4-cyano-4-(thiobenzoyl) sulfanylpentanoic acids, using esterification reaction. This pentablock terpolymer was characterized by 1H NMR, FT-IR, and GPC. The PDI was obtained by GPC, indicating that the molecular weight distribution was narrow and the polymerization was well controlled. The thermo- and pH-responsive micellization of the pentablock terpolymer in aqueous solution was investigated using fluorescence spectroscopy technique, UV–vis transmittance, and TEM. The LCST of pentablock terpolymer increased (over 50 °C) compared to the NIPAM homopolymer (~32 °C), due to the incorporation of the hydrophilic PEG and PMA blocks in pentablock terpolymer (PNIPAM block as the core, PEG the block and the hydrophilic PMA block as the shell and the corona). Also, pH-dependent phase transition behavior shows at a pH value of about ~5.8, according to pKa of MAA. Thus, in acidic solution at room temperature, the pentablock terpolymer self-assembled to form core–shell–corona micelles, with the hydrophobic PMA block as the core, the PNIPAM block and the hydrophilic PEG block as the shell and the corona, respectively.
Highlights
In recent decades, dual responsive copolymers in aqueous solutions have attracted considerable attention, because of its application in gene and drug delivery, polymeric surfactants for stabilization of colloid dispersions and separations
The peak of –NH at 3295 cm−1 and a new peak of a carboxyl group (–OH) became visible at 3439 cm−1 in the spectrum of the pentablock terpolymer, wholly the C–H stretching bonds are observed at 2912 cm−1. All these signals illustrate that the pentablock terpolymer is prepared properly. These results showed that PNIPAM block and poly(methacrylic acid) (PMA) block were connected to chain transfer agent (CTA)–Polyethylene glycol (PEG)–CTA blocks by Reversible addition–fragmentation chain transfer (RAFT)
The pentablock terpolymer was characterized by 1H Nuclear Magnetic Resonance spectroscopy (NMR), Fourier Transform Infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)
Summary
Dual responsive copolymers in aqueous solutions have attracted considerable attention, because of its application in gene and drug delivery, polymeric surfactants for stabilization of colloid dispersions and separations. Responsive polymers show reversible transitions in properties. These polymers are able to undergo a conformational change of phase transition upon the application of an external stimulus such as a change in solution pH, electrolyte concentration or temperature [10,11,12]. Polymer chains can be changed in several ways, such as changes in hydrophilic-to-hydrophobic equilibrium, degradation, conformation, bond. The most important systems, from a chemical and materials science point of view are those sensitive to pH or temperature
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